Man allegedly guns down parents and their 2 friends days after his release from prison

A 34-year-old man allegedly shot and killed his parents and their two friends at a home in Bowdoin, Maine, days after his release from prison, authorities said.

Around 9:21 a.m. Tuesday, four people were found shot dead at the home: 72-year-old Robert Eger, 62-year-old Patricia Eger and 62-year-old Cynthia Eaton were found inside, while 66-year-old David Eaton was found in the barn, Maine State Police said at a news conference Wednesday.

The Eatons' son, Joseph Eaton, had been released from the Windham Correctional Facility in Maine on April 14 after serving a sentence for aggravated assault, according to police. His mother picked him up from prison and brought him to Bowdoin to stay with the Egers, who were family friends, police said.

Shortly after the four bodies were found, around 10:30 a.m. on Tuesday, Joseph Eaton allegedly shot three people as they drove south on Interstate 295 in Yarmouth, about 25 miles south of Bowdoin, police said.

One of the interstate shooting victims, a 25-year-old woman, is in critical condition, police said. The other two victims, a 51-year-old man and his 29-year-old son, suffered non-life-threatening injuries, police said.

Joseph Eaton was taken into custody and "confessed to killing his parents and their friends in Bowdoin," state police said. Joseph Eaton allegedly "believed that the vehicles he had shot on the interstate were police vehicles that were following him."

He has been charged with four counts of murder, police said.

Joseph Eaton made his first appearance in court on Thursday morning. He spoke briefly, only to say he understood the charges against him, and did not enter a plea.

ABC News' Darren Reynolds and Ben Stein contributed to this report.